U.S. patent application number 17/276466 was filed with the patent office on 2022-02-03 for void fraction calibration method.
The applicant listed for this patent is M-Flow Technologies Limited. Invention is credited to Giles Edward, Alan David Parker.
Application Number | 20220034777 17/276466 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-03 |
United States Patent
Application |
20220034777 |
Kind Code |
A1 |
Parker; Alan David ; et
al. |
February 3, 2022 |
Void Fraction Calibration Method
Abstract
A method produces a void fraction (VF) error curve which
correlates an apparent VF with the actual VF of a multi-phase flow,
the method comprising (a) using a device to measure a property of
the multi-phase flow from which an apparent VF may be calculated;
(b) calculating the apparent VF using the measured property from
the device; (c) determining the actual VF of the multiphase flow
using a radiometric densitometer; (d) using the values from steps
(b) and (c) to calculate the VF error; (e) repeating steps (b)
through (d) for all expected flow conditions to generate a VF error
curve.
Inventors: |
Parker; Alan David;
(Abingdon, GB) ; Edward; Giles; (Abingdon,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
M-Flow Technologies Limited |
Abingdon |
|
GB |
|
|
Appl. No.: |
17/276466 |
Filed: |
September 11, 2019 |
PCT Filed: |
September 11, 2019 |
PCT NO: |
PCT/GB2019/052531 |
371 Date: |
March 15, 2021 |
International
Class: |
G01N 9/36 20060101
G01N009/36; G01F 1/74 20060101 G01F001/74; G01F 1/84 20060101
G01F001/84; G01F 25/00 20060101 G01F025/00; G01N 22/00 20060101
G01N022/00; G01N 23/12 20060101 G01N023/12; G01N 33/28 20060101
G01N033/28; G01N 9/00 20060101 G01N009/00; G01F 1/40 20060101
G01F001/40 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2018 |
GB |
1814910.4 |
Claims
1-17. (canceled)
18. A method of producing a void fraction (VF) error curve which
correlates an apparent VF with the actual VF of a multi-phase flow,
the method comprising: (a) Using a device to measure a property of
the multi-phase flow from which an apparent VF may be calculated;
(b) Calculating the apparent VF using the measured property from
the device; (c) Determining the actual VF of the multiphase flow
using a radiometric densitometer; (d) Using the values from steps
(b) and (c) to calculate the VF error; (e) Repeating steps (b)
through (d) for all expected flow conditions to generate a VF error
curve.
19. A method of calculating the actual VF of a multiphase flow
comprising measuring a property of the flow from which an apparent
VF may be calculated, calculating the apparent VF of the multiphase
flow and correcting the apparent VF using the VF error curve of
claim 18.
20. The method of claim 18, wherein the radiometric densitometer is
an X-ray densitometer or a gamma densitometer.
21. The method of claim 18, wherein the flow comprises a liquid
phase and a gas phase.
22. The method of claim 21, wherein the liquid phase comprises a
water phase and an oil phase.
23. The method of claim 18, wherein the device is a Coriolis meter
and the measured property is the apparent bulk density of the
multiphase flow.
24. The method of claim 18, wherein the device is a microwave
meter, preferably a microwave resonator, and the measured property
is the permittivity of the multiphase flow.
25. A method for calculating the mass flow rate of one or more of
the phases in a multiphase flow comprising: (a) Using a Coriolis
meter to measure the apparent bulk density of the multiphase flow;
(b) Calculating a first apparent VF using the apparent bulk density
from step (a); (c) Using a microwave meter to measure the
permittivity of the multiphase flow; (d) Calculating a second
apparent VF using the permittivity measurement from step (c); (e)
Calculating the phase volume fractions of the multiphase flow using
the results from steps (b) and (d), wherein the VF error curves of
claims 23 and 24 are additionally used to improve the calculation;
(f) Determining the actual bulk mass flow rate of the multiphase
flow; and (g) Calculating the mass flow rate of one or more of the
phases using the values from steps (d) and (e).
26. The method of claim 25, wherein the multiphase flow comprises a
liquid phase and a gas phase.
27. The method of claim 25, wherein the multiphase flow comprises
oil and the method comprises calculation of the oil phase mass flow
rate.
28. The method of claim 25, wherein step (f) determining the actual
bulk mass flow rate comprises: (i) measuring the differential
pressure across the Coriolis meter using a differential pressure
meter; (ii) determining the liquid mass flow rate through the
Coriolis meter using the differential pressure value from step (i);
and (iii) Using the liquid mass flow rate from step (ii), the known
phase volume fractions and the actual bulk density of the
multiphase flow to calculate the actual bulk mass flow rate;
wherein the actual bulk density is calculated by correcting the
apparent bulk density using a bulk density error curve.
29. The method of claim 25, wherein step (e) determining the actual
bulk mass flow rate for a multiphase flow comprises: (i)
determining the bulk mass flow rate error from the bulk density
error; and (ii) calculating the actual bulk mass flow rate by
correcting the apparent bulk mass flow rate using the bulk mass
flow rate error, wherein the actual bulk density is calculated by
correcting the apparent bulk density using a bulk density error
curve.
30. A metering arrangement for measuring the mass flow rate of one
or more of the phases in a multiphase flow, the metering
arrangement comprising: (a) a Coriolis meter for measuring the
apparent bulk density and the apparent bulk mass flow rate of the
multiphase flow; (b) a differential pressure meter for measuring
the differential pressure across the Coriolis meter; (c) a
microwave meter, preferably a microwave resonator, for measuring
the bulk permittivity of the multiphase flow; and (d) a computation
device to: (i) Calculate a first apparent VF from the apparent bulk
density; (ii) Calculate a second apparent VF from the bulk
permittivity; (iii) Calculate the phase volume fractions of the
multiphase flow using the results from steps (i) and (ii); (iv)
determine the liquid mass flow rate of the multiphase flow using
the differential pressure measured by the differential pressure
meter; (v) calculate the actual bulk mass flow rate of the
multiphase flow; (vi) calculate the mass flow rate of one or more
of the phases in the multiphase flow.
31. The apparatus of claim 30, wherein calculating the phase volume
fractions of the multiphase flow in step (iii) includes using a
first and a second VF error curve correlating the first apparent VF
and the second apparent VF to the actual VF determined using a
radiometric densitometer.
32. The apparatus of claim 31, wherein the computation device is
located proximate to or remotely from the metering arrangement.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for calibrating a
void fraction measurement made in relation to a multiphase flow and
to a method and apparatus for calculating the mass flow rate of one
or more phases in a multiphase flow.
DESCRIPTION OF THE RELATED ART
[0002] The extraction of hydrocarbons is known to present many
challenges. One of the challenges is to establish the phase
fractions of the materials extracted from a well, when the flow of
extracted materials may comprise up to three phases (a liquid oil
phase, a liquid aqueous phase and a gaseous phase). Not only may
the volume fractions of the phases change with time, but the
distribution of the phases in the flow may also change. In
particular, the distribution of any gaseous phase present may
change as a result of the flow environment, the presence of bends
in the pipe and other factors. Part of the flow may comprise a
relatively homogenous distribution of small bubbles, while in
another part the coalescence of gas bubbles may result in a
heterogeneous distribution of the gaseous phase. Changes in the
pressure and temperature may also cause materials, such as volatile
hydrocarbons, to move between the liquid and gaseous phases. It is
important to know the mass flow rate of the extracted hydrocarbons,
since oil extraction is the whole purpose of the business.
[0003] One method of addressing this problem is to provide flow
meters downstream of two or three-phase separator(s), then
separately to measure the flow of each of the phases. The
separators may be large, expensive and maintenance-intensive. In
addition, if the separator(s) are incorrectly sized, then a
materially significant amount of gas may remain entrained in the
output liquid phase(s) or water in the oil output of a three phase
separator. Separator sizing requirements can change as a well ages
and it is often not practical or economically viable to replace a
separator during the life of an individual well.
[0004] Multiphase meters capable of determining the phase volume
fractions may employ several different measurement methods to
achieve the objective. One such method involves using a device
which is sensitive to changes in the permittivity of the flow, such
as a microwave resonator and, separately, measuring the density of
the combined flow. An apparatus suitable for carrying out these
measurements is disclosed in WO 2016/135506 A1 and involves passing
the fluid flow through a resonant cavity microwave meter and
additionally measuring the bulk density of the flow by means of a
gamma densitometer.
[0005] Radiometric densitometers, such as gamma and x-ray
densitometers, although accurate, require the use of a hazardous
radioactive source, which in turn gives rise to health and safety
concerns and necessitates significant shielding. This can make such
meters heavy, cumbersome and costly. In addition, special
certification and other procedures are needed before a radioactive
source may be used on site, which are time-consuming and costly to
organize.
[0006] Coriolis meters are known for the measurement of mass flow
rate and density. Such meters comprise tubes that are vibrated at
their natural frequency. When no flow is present, the tubes vibrate
in phase and show no sign of twist. Once a flow is introduced,
Coriolis forces give rise to a twisting effect in the tubes. By
measuring the time shift in phase of oscillation of each measuring
tube, a mass flow rate may be calculated, and by measuring the
natural frequency of oscillation of one of the measuring tubes, the
density may be calculated.
[0007] In principle, Coriolis meters represent a safer and less
bulky alternative to radiometric densitometers for measuring the
bulk density of a flow and they have the additional benefit of
measuring the mass flow rate as well. In practice, however,
Coriolis meters may give inaccurate readings of both bulk density
and mass flow rate if there are phases of significantly different
density and/or viscosity present such that there is poor coupling
between the dispersed and continuous phases, an effect which may be
referred to as "phase contamination". The problem may be especially
significant when the flow comprises mixtures of liquid and gaseous
phases. The introduction of gas into a liquid flowing through a
Coriolis meter significantly dampens the amplitude and distorts the
phase of the tube oscillations. These changes lead to errors in
both the mass flow and the density data from the meter. In general,
the measurement error is dependent upon a number of parameters,
such as the liquid velocity and viscosity, the pressure and
temperature of the flow and the degree of entrainment of the gas in
the liquid. If the gas decouples from the liquid, such that it is
no longer entrained, then so-called "slug flow" may result, which
may increase the measurement errors. These factors, which are all
variable, may make it difficult to compensate for the measurement
errors in the field. Reference may be made to the paper by Chris
Mills entitled "Correcting a Coriolis Meter for Two Phase Oil &
Gas Flow", presented at the International Flow Measurement
Conference 2015 from 1-2 Jul. 2015 at the University of Warwick,
UK.
[0008] For 3-phase flow in hydrocarbon extraction (comprising an
oil phase, a water phase and a gaseous phase), if the gas to liquid
ratio and the fluid velocity is relatively constant and known, then
an approximate correction factor may be applied which may allow the
Coriolis meter to output a relatively accurate density and mass
flow rate. If, on the other hand, these quantities fluctuate
significantly, then this approach does not provide an accurate bulk
density and mass flow rate.
[0009] It is against this background that the present invention has
been devised.
SUMMARY OF THE INVENTION
[0010] According to a first aspect of the invention, a method is
provided of producing a void fraction (VF) error curve which
correlates an apparent VF with the actual VF of a multi-phase flow,
the method comprising: [0011] a) Using a device to measure a
property of the multi-phase flow from which an apparent VF may be
calculated; [0012] b) Calculating the apparent VF using the
measured property from the device; [0013] c) Determining the actual
VF of the multiphase flow using a radiometric densitometer; [0014]
d) Using the values from b) and c) to calculate the VF error;
[0015] e) Repeating b)-d) for all expected flow conditions to
generate a VF error curve.
[0016] As used herein, the term "VF" of a fluid flowing through a
pipe, means:
VF=Volume of gas in unit volume of pipe
at the prevailing conditions of temperature and pressure in the
pipe. It is usually expressed as a percentage.
[0017] As used herein, the term "water cut" (WC) has the following
meaning:
WC = Volume .times. .times. of .times. .times. water .times.
.times. in .times. .times. unit .times. .times. volume .times.
.times. of .times. .times. pipe Volume .times. .times. of .times.
.times. liquid .times. .times. in .times. .times. unit .times.
.times. volume .times. .times. of .times. .times. pipe
##EQU00001##
at the prevailing conditions of temperature and pressure in the
pipe. It is also usually expressed as a percentage.
[0018] The radiometric densitometer may suitably be any meter which
measures the true density of the flow, such as a gamma densitometer
or an x-ray densitometer. The radiometric densitometer may be a
dual energy densitometer or a single energy densitometer.
[0019] The actual VF may be determined directly from the
radiometric densitometer, if the radiometric densitometer is a dual
energy or DEGRA (dual energy gamma ray attenuation) densitometer,
which uses both a high energy and a low energy radiation source
firstly to distinguish the gas from the liquid, then the oil from
the water. If the radiometric densitometer is a single energy
densitometer, then the actual VF may not be obtained directly and
must be calculated. The calculation may be performed using the
actual bulk density measured by the radiometric densitometer.
Equation 1, below, may be used (substituting the apparent bulk
density by the actual bulk density, measured by the radiometric
densitometer, to give the actual VF).
[0020] According to a second aspect of the invention, a method of
calculating the actual VF of a multiphase flow comprising measuring
a property of the flow from which an apparent VF may be calculated,
calculating the apparent VF of the multiphase flow and correcting
the apparent VF using the VF error curve of the first aspect of the
invention.
[0021] The method according to the first and second aspects of the
invention may advantageously be used when the flow comprises a
liquid phase and a gas phase. More advantageously, the liquid phase
may comprise a water phase and an oil phase such that there is a
3-phase flow comprising a mixed oil and aqueous liquid phase and a
gaseous phase.
[0022] According to one embodiment of the first and second aspects
of the invention, the device which measures a property of the
multi-phase flow from which an apparent VF may be calculated is a
Coriolis meter. Coriolis meters measure an apparent bulk density
and an apparent mass flow. The apparent bulk density measurement
may be used to derive the apparent VF using Equation 1:
Apparent .times. .times. VF = .rho. L - .rho. .rho. L - .rho. g
Equation .times. .times. 1 ##EQU00002##
where .rho..sub.L is the density of the liquid, .rho..sub.G is the
density of the gas and p is the apparent bulk density measured by
the Coriolis meter.
[0023] During this calibration phase, .rho..sub.L and .rho..sub.G
may be obtained by actual measurements taken from samples extracted
from the flow line to determine the phase fractions and, if needed,
data known to the skilled person from models, such as "PVT Models"
(where "PVT" relates to pressure, volume and temperature).
[0024] According to another embodiment of the first and second
aspects of the invention, the device which measures a property of
the multi-phase flow from which an apparent VF may be calculated is
a microwave meter. The microwave meter may use resonance (a
"microwave resonator") or absorption. Preferably, the microwave
meter is a microwave resonator such as disclosed in WO 2016/135506
A1. A microwave meter may measure the bulk permittivity of the
multiphase flow from which an apparent VF may be derived in a
fashion known to the skilled person.
[0025] The first and second aspects of the invention relate to the
calibration of the device or devices from which an apparent VF may
be derived. According to these aspects of the invention, the device
such as a Coriolis meter and/or a microwave meter is installed in a
flow line in the field and, additionally, a radiometric
densitometer is also temporarily installed. The applicant's
preferred approach is to calibrate the device in situ in the actual
line in the field into which it is to be permanently installed. The
device is calibrated for the entire operating envelope of the line
in question. This means that a bulk density and VF error curves are
generated for all expected full range of flow conditions seen by
the line. The time required to do this will vary between wells but
typically will be a number of days.
[0026] Once calibration has been performed, the device(s) may be
monitored in use in the fashion discussed below to ensure
continuing accuracy, so it is straightforward to verify the
calibration.
[0027] Once VF error curve(s) have been generated for the device(s)
in question, such as a Coriolis meter or a microwave meter, then
the radiometric densitometer may be removed leaving just the
device(s) which may thereafter be used together with the VF error
curve(s) accurately to determine the actual VF of the multiphase
flow.
[0028] According to a third aspect of the invention, a method is
provided for calculating the mass flow rate of one or more of the
phases in a multiphase flow comprising: [0029] a) Using a Coriolis
meter to measure the apparent bulk density of the multiphase flow;
[0030] b) Calculating a first apparent VF using the apparent bulk
density from a); [0031] c) Using a microwave meter to measure the
permittivity of the multiphase flow; [0032] d) Calculating a second
apparent VF using the permittivity measurement from c); [0033] e)
Calculating the phase volume fractions of the multiphase flow using
the results from b) and d); [0034] f) Determining the actual bulk
mass flow rate of the multiphase flow; [0035] g) Calculating the
mass flow rate of one or more of the phases using the values from
d) and e).
[0036] According to the third aspect of the invention, a Coriolis
meter measures the apparent bulk density and the apparent bulk mass
flow rate of the multiphase flow. A first apparent VF is then
calculated using Equation 1, above. After this, a microwave meter
measures the bulk permittivity of the multiphase flow. A second
apparent VF is calculated from the bulk permittivity
measurement.
[0037] The two apparent VF measurements may be used to calculate
the WC of the multiphase flow and therefore also the phase volume
fractions (since knowing the WC and the VF allows calculation of
the phase fractions). Both the bulk permittivity measurement from
the microwave meter and the bulk density measurement from the
Coriolis meter are sensitive to the VF and the WC of the multiphase
flow. A specific pair of values from the two parameters (apparent
bulk density and bulk permittivity) can be generated for a range of
WC and VF values. The true WC and VF of the multiphase fluid in the
meter arrangement can be determined by calculating the VF for a
range of WC values from the measurement taken from each meter (one
from the microwave meter and one for the Coriolis meter) and
finding the water cut value for which both measurements give an
identical void fraction.
[0038] This process may be represented by two curves on a two
dimensional plot of WC versus VF. Each curve represents the
possible values of WC and VF that could lead to a particular
measurement value from either the microwave meter or bulk density
data from the Coriolis meter. The true WC and VF values occur where
these two curves cross.
[0039] The microwave data is predominantly sensitive to the water
cut and the bulk density is predominantly sensitive to the void
fraction. Thus the two curves from the different measurements are
typically close to perpendicular to each other which means that the
crossing point is sharply defined.
[0040] In an advantageous development, the VF error curves from the
first aspect of the invention may be used for the calculation in
e). In this case, a solution is found by iteration or by solving
simultaneous equations so that the measurements from the Coriolis
meter and the measurement from the microwave meter both yield the
actual VF measured by the radiometric densitometer. On a
two-dimensional plot of WC versus VF, the actual WC may then be
determined.
[0041] According to the third aspect of the invention, the actual
bulk mass flow rate of the multiphase flow must be calculated. The
relationship between the differential pressure across an
obstruction within a pipe and the mass flow rate of the material
flowing through it for an incompressible fluid is known from
Bernoulli's Principle. Thus one method for establishing the mass
flow rate of material flowing through the pipe is by means of a
differential pressure measurement across an obstruction to the flow
within the pipework. Differential pressure meters based on this
principle are well known and include Venturi and orifice plate
devices. These may be used to measure the pressure drop along a
section of a fluid flow path, for example along a length of pipe,
or across a device. A Coriolis meter provides an obstruction to the
flow within a pipe so the differential pressure across a Coriolis
meter may be used to measure the mass flow rate through the
meter.
[0042] The Bernoulli relationship between differential pressure
across and the mass flow rate through an obstruction within a pipe
would not be expected to apply to a multiphase flow containing a
gaseous phase, as this type of fluid will be compressible. i.e. the
line density will vary with pressure. However the applicant has
established that, if the amount of gas present is less than 5%,
preferably less than 2% and more preferably less than 1% by mass of
the multiphase fluid, then the pressure drop for a given mass flow
rate of liquid-only flow is the same as the pressure drop for same
mass flow rate of a multiphase flow including a gaseous phase. In
other words, the differential pressure is primarily dependent upon
the liquid mass flow rate and is independent of the VF.
Installation of a device to measure the differential pressure may
therefore allow an accurate determination of the liquid mass flow
rate even for a multiphase flow containing a gaseous phase.
[0043] According to the third aspect of the invention, therefore, a
differential pressure meter is provided to measure the differential
pressure across the Coriolis meter in order to allow the mass flow
rate of the liquid within the pipe to be established.
[0044] The relationship between the mass flow rate of a liquid only
flow of known density through a Coriolis meter and the differential
pressure across it is an important operational parameter for many
Coriolis meter installations and is likely to be known by the
manufacturer. If not, it may easily be established in any case.
Given that the applicant has now established that this information
may be used for a multiphase flow comprising a gaseous phase, the
differential pressure may advantageously be measured across the
Coriolis meter and information provided with the Coriolis meter may
be used to correlate the measured differential pressure across the
meter with the liquid mass flow rate through it.
[0045] In order to calculate the actual mass flow rate, the actual
bulk density of the multiphase flow must be known. This may be
derived from a bulk density error curve which corrects the apparent
bulk density measured by the Coriolis meter with the actual bulk
density. A radiometric densitometer, such as that described in
relation to the first aspect of the invention, may be used to
measure the actual bulk density of the multiphase flow. Thus a bulk
density error curve may be generated in parallel with generation of
the VF error curve for the Coriolis meter according to the first
aspect of the invention.
[0046] Knowing the actual bulk density from the Coriolis meter,
corrected using the bulk density error curve and the phase volume
fractions of the multiphase flow (generated using the Coriolis
meter and the microwave meter and, advantageously, also the VF
error curves of the first aspect of the invention) and the mass
flow rate of the liquid using a differential pressure measurement
across the Coriolis meter, the actual bulk mass flow rate may be
calculated.
[0047] Using a differential pressure measurement allows the actual
liquid mass flow rate to be determined in flow regimes of varying
liquid phase velocity. In cases in which the liquid phase velocity
is relatively constant, then there is a linear relationship between
the bulk mass flow rate error and the bulk density error, so that
an alternative method may be used, wherein calculating the actual
bulk mass flow rate for a multiphase flow comprises: [0048] i.
determining the bulk mass flow rate error from the bulk density
error; and [0049] ii. calculating the actual bulk mass flow rate by
correcting the apparent bulk mass flow rate using the bulk mass
flow rate error. wherein the actual bulk density is calculated by
correcting the apparent bulk density using a bulk density error
curve.
[0050] Finally, according to the third aspect of the invention, the
actual mass flow rate of one or more of the phases in the
multiphase flow is then calculated. This is done using the phase
volume fractions and the actual bulk mass flow rate. For
completeness, the density of each of the individual phases at the
given temperature and pressure must also be known, but this is
information that the skilled person readily has available, for
example from a PVT model.
[0051] Advantageously, according to the third aspect of the
invention, the multiphase flow comprises water, oil and gas and the
method comprises calculating the volume fractions of each of these
phases. A further advantageous development according to the third
aspect of the invention comprises calculating the mass flow rate of
oil.
[0052] The third aspect of the invention allows accurate
determination of the mass flow rate(s) of one or more of the phases
in a multiphase flow using just a Coriolis meter, meter, a
microwave meter and, optionally, a differential pressure meter
installed in situ in a working line. It avoids the need for
permanent installation of a radiometric densitometer.
[0053] An important advantage of the present invention is that,
following calibration of the Coriolis meter and the microwave
meter, the accuracy of these meters may be monitored in a simple
fashion. As part of a regular, scheduled calibration and/or if a
significant change in the flow conditions is believed to have
occurred, the performance of these meters may be assessed by taking
a sample of the liquid from the multiphase flow in the line,
analyzing it to establish the proportions of each liquid phase
present, such as oil and water, and comparing this with the WC
reading derived from the combination of the Coriolis meter and the
microwave meter. As the VF and WC data generated by these two
meters are interdependent, if the WC measurement from the meter is
accurate, then the VF will also be accurate.
[0054] According to a fourth aspect of the invention, a metering
arrangement is provided for calculating the mass flow rates of one
or more of the phases in a multiphase flow, the metering
arrangement comprising: [0055] a) a Coriolis meter for measuring
the apparent bulk density and the apparent bulk mass flow rate of
the multiphase flow; [0056] b) a differential pressure meter for
measuring the differential pressure across the Coriolis meter;
[0057] c) a microwave meter, preferably a microwave resonator, for
measuring the bulk permittivity of the multiphase flow.
[0058] The apparatus according to the fourth aspect of the
invention may advantageously comprise a computation device
configured to: [0059] a) Calculate a first apparent VF from the
apparent bulk density; [0060] b) Calculate a second apparent VF
from the bulk permittivity; [0061] c) Calculate the phase volume
fractions of the multiphase flow using the results from a) and b);
[0062] d) determine the liquid mass flow rate of the multiphase
flow using the differential pressure measured by the differential
pressure meter; [0063] e) calculate the actual bulk mass flow rate
of the multiphase flow; [0064] f) calculate the mass flow rate of
one or more of the phases in the multiphase flow.
[0065] Advantageously, according to the fourth aspect of the
invention calculating the phase volume fractions of the multiphase
flow in step c) includes using a first and a second VF error curve
correlating the first apparent VF and the second apparent VF to the
actual VF determined using a radiometric densitometer.
[0066] According to the fourth aspect of the invention, the
computation device may be located proximate to the metering
arrangement or it may be located remotely from the metering
arrangement. In either case, the connection between the metering
arrangement and the computation device may be hard-wired or it may
operate wirelessly.
[0067] The computation device according to preferred embodiments is
described as configured or arranged to, or simply "to" carry out
certain functions. This configuration or arrangement could be by
use of hardware or middleware or any other suitable system. In
preferred embodiments, the configuration or arrangement is by
software.
[0068] Thus according to one aspect there is provided a program
which, when loaded onto at least one computer configures the
computer to become the computation device.
[0069] According to a further aspect there is provided a program
which when loaded onto the at least one computer configures the at
least one computer to carry out the method steps according to any
of the preceding method definitions or any combination thereof.
[0070] In general the computer may comprise the elements listed as
being configured or arranged to provide the functions defined. For
example this computer may include memory, processing, and a network
interface.
[0071] The invention may be implemented in digital electronic
circuitry, or in computer hardware, firmware, software, or in
combinations of them. The invention may be implemented as a
computer program or computer program product, i.e., a computer
program tangibly embodied in a non-transitory information carrier,
e.g., in a machine-readable storage device, or in a propagated
signal, for execution by, or to control the operation of, one or
more hardware modules.
[0072] A computer program may be in the form of a stand-alone
program, a computer program portion or more than one computer
program and may be written in any form of programming language,
including compiled or interpreted languages, and it may be deployed
in any form, including as a stand-alone program or as a module,
component, subroutine, or other unit suitable for use in a data
processing environment. A computer program may be deployed to be
executed on one module or on multiple modules at one site or
distributed across multiple sites and interconnected by a
communication network.
[0073] Method steps of the invention may be performed by one or
more programmable processors executing a computer program to
perform functions of the invention by operating on input data and
generating output. Apparatus of the invention may be implemented as
programmed hardware or as special purpose logic circuitry,
including e.g., an FPGA (field programmable gate array) or an ASIC
(application-specific integrated circuit).
BRIEF DESCRIPTION OF THE DRAWINGS
[0074] FIG. 1 illustrates an arrangement according to the invention
in calibration mode, which enables a device, such as a Coriolis
meter or a microwave meter, to be calibrated by means of a
radiometric densitometer.
[0075] FIG. 2 illustrates a metering arrangement according to the
invention in an in-use mode for measuring the mass flow rate of one
or more of the phases in a multiphase flow.
[0076] FIG. 3 is a flow chart illustrating the method of the first
aspect of the invention.
[0077] FIG. 4 is a flow chart illustrating the method of the third
aspect of the invention.
[0078] FIG. 5 is a graph showing the relationship between VF and WC
for both a Coriolis resonator and a microwave meter.
[0079] FIG. 6 is a curve showing the GVF measured by the Coriolis
meter (y-axis) and microwave meter against the GVF measured by the
gamma densitometer (x-axis).
[0080] FIG. 7 is a curve showing the differential pressure across
the Coriolis meter in bar (y-axis) against the liquid velocity
through the Coriolis meter in m/s (x-axis).
[0081] The drawings will now be discussed in more detail:
[0082] FIG. 1 figuratively illustrates an arrangement for
calibrating a device which measures the property of a multiphase
flow from which an apparent VF may be calculated, such as a
Coriolis meter or a microwave meter. The calibration is by means of
a radiometric densitometer. The arrangement comprises a flow line 1
through which a multiphase flow F passes. The device 2 and a
radiometric densitometer 5 are installed in the flow line 1.
Instrumentation lines 6 connect each of the device 2 and the
radiometric densitometer 5 with a computational device 7. It is
possible to perform the calibration on more than one device 2 at a
time. For example, two devices 2, such as a Coriolis meter and a
microwave meter, may be placed in the flow line 1 and both may be
calibrated using the radiometric densitometer 5. Such calibrations
may be performed simultaneously or one after the other.
[0083] If the device 2 is a Coriolis meter, then the property that
it measures is the apparent density of the multiphase flow, F. For
completeness, a Coriolis meter may also measure the apparent mass
flow of the multiphase flow. The radiometric densitometer 5
measures the actual density of the multiphase flow. If the
radiometric densitometer is a dual energy device, then it may also
directly determine the actual VF of the multiphase flow, F. The
readings from both meters are fed to the computation device 7 which
calculates the apparent VF using the apparent bulk density
measurement from the Coriolis meter. If necessary (if the
radiometric densitometer is not a dual energy device), the
computational device 7 also calculates the actual VF using the
actual bulk density measurement from the radiometric densitometer.
The computational device 7 may also generate a density error curve
allowing correction of the apparent bulk density, as measured by
the Coriolis meter 2, to the actual bulk density, as measured by
the radiometric densitometer.
[0084] If the device 2 is a microwave meter, then the property that
it measures is the bulk permittivity of the multiphase flow, F.
Again, the radiometric densitometer 5 measures the actual density
of the multiphase flow, F. The readings from both meters are fed to
the computation device 7 which calculates the apparent VF using the
bulk permittivity measurement from the microwave meter. If
necessary (if the radiometric densitometer is not a dual energy
device), the computational device 7 also calculates the actual VF
using the actual bulk density measurement from the radiometric
densitometer.
[0085] The arrangement of FIG. 1 functions as shown in the flow
diagram of FIG. 3. At 10, a device 2 is used to measure a property
of a multiphase flow, F, from which an apparent VF may be
calculated. At 20, an apparent VF is measured using the device. At
30 the actual VF of the multiphase flow, F, is determined using a
radiometric densitometer. At 40 the error in the VF error is
calculated, which is the difference between the actual VF, measured
by the radiometric densitometer 5, and the apparent VF, measured by
the device 2. These steps are repeated for all expected flow
conditions at 50 in order to generate a VF error curve for the
entire operating envelope of the line in question.
[0086] FIG. 2 figuratively illustrates an arrangement for measuring
the mass flow rate of one or more of the phases in a multiphase
flow F in an in-use condition following calibration using the
arrangement of FIG. 1. The arrangement of FIG. 2 comprises a flow
line 1 through which a multiphase flow F passes. A Coriolis meter 8
has been installed in the line and, either side of the Coriolis
meter 8, is a pressure sensor 3, which together measure the
differential pressure across the Coriolis meter 8. In addition, a
microwave meter 4 is installed in the flow line 1. Instrumentation
lines 6 connect each of the Coriolis meter 8, the pressure sensors
3 and the microwave meter 4 with a computational device 7. In this
arrangement, the VF error curves for the Coriolis meter 8 and the
microwave meter 4 and a bulk density error curve for the Coriolis
meter 8 have previously been produced using the arrangement
according to FIG. 1 and are stored in computational device 7.
Computational device 7 is therefore able to correct the apparent VF
measured by both the Coriolis meter 8 and the microwave meter 4 to
the actual VF, as previously measured by the radiometric
densitometer 5. It may also store a bulk density error curve
allowing correction of the apparent bulk density measured by the
Coriolis meter 8 to the actual bulk density, as also previously
measured by the radiometric densitometer 5, and thereby calculate
the actual bulk density of the multiphase flow.
[0087] The arrangement of FIG. 2 functions as shown in the flow
diagram of FIG. 4. At 60 the apparent bulk density is measured by
the Coriolis meter 8. In addition, although not shown, the apparent
mass flow rate may also be measured. At 70, the first apparent VF
of the multiphase flow is calculated using the apparent bulk
density measured by the Coriolis meter 8. At 80, the permittivity
of the multiphase flow is measured using a microwave meter 4. At 90
the second apparent VF is calculated using the permittivity
measurement from the microwave meter. The outputs from 70 and 90
are used to generate the phase volume fractions of the multiphase
flow at 100. At 110, the actual bulk mass flow is generated using
the output from the pressure sensors. Alternatively, in flow
regimes in which the liquid velocity is relatively constant, this
may be performed by correcting the apparent bulk mass flow rate
measured by the Coriolis meter 8 using the bulk density error curve
and determining the bulk mass flow rate error from the bulk density
error, in the fashion explained above. Finally, at 120 the mass
fraction(s) of one or more of the phases are calculated.
[0088] FIG. 5 is a schematic graph illustrating how the first and
second apparent VF data may be used to determine the phase volume
fractions:
[0089] Curve A, which is the line with the arrow that is in a
predominantly vertical direction represents the possible values of
VF and WC that correspond to a particular microwave meter mode
frequency measurement. This line is in a predominantly vertical
direction as this measurement is primarily sensitive to the WC.
This is because the electrical permittivity of water is much higher
than those of oil and gas, which are similar.
[0090] Curve B, which is the line with the arrow that is in a
predominantly horizontal direction, represents the possible pairs
of VF and WC values that correspond to a particular apparent bulk
density value measured by the Coriolis meter. For an assumed water
cut value the VF is calculated from Equation 1 which is repeated
here for convenience:
Apparent .times. .times. VF = .rho. L - .rho. .rho. L - .rho. g
Equation .times. .times. 1 ##EQU00003##
Where:
[0091] .rho..sub.L is the liquid density. This is calculated from
the known oil and water densities and the assumed WC .rho..sub.G is
the density of the gas, which is determined from a PVT Model .rho.
is the apparent bulk density measured by the Coriolis meter.
[0092] This line is predominantly horizontal as this measurement is
primarily sensitive to changes in the VF of gas due to the fact
that the gas density is much lower than the densities of oil and
water.
[0093] The method used calculates the VF fraction values that are
possible for a range of WC cut values from each measurement (one
from the Coriolis meter and one from the microwave meter) and plots
these two curves from the results of these calculations. The point
at which the two lines cross is the point at which the VF
calculated from each measurement is the same. As both lines are
monotonic functions (you cannot have the same calculated VF value
for two different WC values) the WC at which the lines cross is the
actual WC value, marked as point "c" in FIG. 5. This point may be
found using either iterative methods or analytically by solving a
pair of simultaneous linear equations.
[0094] The method described above may become inaccurate if phase
contamination occurs. In such a situation, the apparent bulk
density measured by the Coriolis meter may become inaccurate. More
specifically, the Coriolis meter may over-read the bulk density and
a correction is needed to this value to obtain the equivalent VF
from the microwave meter. At most VF values, the microwave VF
determined from the microwave meter is closer to the actual VF
measured by the radiometric densitometer than the VF derived from
the Coriolis density data.
[0095] In order to address this situation, a calibration is
performed using a radiometric densitometer in order to obtain the
error curves between the apparent VF measured by the Coriolis meter
and the actual VF measured by the radiometric densitometer on the
one hand, and the apparent VF measured by the microwave meter and
the actual VF measured by the radiometric densitometer on the other
hand. The curves shown in FIG. 6 illustrate the relationships found
using the test apparatus described below. Using the error curves,
the actual WC of a given multiphase flow may be found by iterating
or solving simultaneous equations so that both the measurement from
the Coriolis meter and the measurement from the microwave meter
yield the actual VF as determined by the radiometric densitometer.
This method may give an accurate WC and VF, including in situations
in which there is phase contamination.
[0096] A test apparatus according to the invention comprised the
following devices: [0097] 1. An M-Flow Technologies Ltd. microwave
resonator [0098] 2. An Endress and Hauser Promass Q500, which is a
commercially available Coriolis meter suitable for measuring 2
phase liquid flow (such as water-in-oil). [0099] 3. Two commercial
pressure sensors, one placed either side of the Coriolis meter.
[0100] 4. A multiphase gamma densitometer manufactured by M-Flow
Technologies Ltd. This consists of a gamma source and receiver
provided by Berthold Technologies (Berthold LB6775 and source is
LB-7440-F-CR) which are mounted outside a piece of composite pipe.
The device is a full pipe gamma densitometer (the gamma beam covers
the full width of the pipe) and is capable of measuring the line
density of the multiphase flow. It is a single energy device.
[0101] Devices 1, 2 and 3 were permanently installed parts of the
apparatus. Device 4, the gamma densitometer, was installed
temporarily to calibrate the density measured by the Coriolis
meter.
[0102] The relevant test section of the apparatus consisted of a
predominantly vertically aligned section in which the microwave
resonator, the gamma densitometer and the Coriolis meter were
connected in series in the flow path and in this order in the flow
direction. In addition, a pressure sensor was connected either side
of the Coriolis meter in the flow direction.
[0103] Multiphase flow mixtures of water, oil and gas were pumped
through the test section in exactly known proportions and the water
cut, the VF and the superficial velocities were varied.
[0104] The apparent bulk density was measured by the Coriolis meter
and the bulk permittivity was measured using the microwave
resonator and an apparent VF is derived from both sets of data. At
the same time, the actual VF was determined from the gamma
densitometer (which is a single energy densitometer) and the
relationships between the actual VF, measured by the gamma
densitometer, and the apparent VF values determined from the
Coriolis apparent bulk density and the microwave permittivity
readings were determined. This step was performed for all flow
conditions in order to obtain error curves for the entire operating
envelope.
[0105] The error curves are shown in FIG. 6. At the same time, a
bulk density error curve (not shown) was generated, correlating the
apparent bulk density measured by the Coriolis meter with the
actual bulk density measured by the radiometric densitometer for
the entire operating envelope.
[0106] After this calibration, the radiometric densitometer was no
longer required.
[0107] In use, the phase volume fractions were determined as
discussed above
[0108] To generate an oil mass flow rate, the actual mass flow rate
of the multiphase flow must be measured. As previously discussed,
this would traditionally be obtained from the Coriolis meter on its
own, because one function of this type of meter is to measure mass
flow. As also discussed, when a gaseous phase is present in the
multiphase flow, the mass flow measurement performance of a
Coriolis meter deteriorates and it is challenging to compensate for
the errors that occur.
[0109] The applicant has established that, at low mass percentages
of gas, the differential pressure across the Coriolis meter is
primarily dependent on the liquid velocity through the meter.
Measurements from the test section described above demonstrate
this. With reference to FIG. 7, it can be seen that the
relationship between differential pressure and liquid velocity is
the same for VF of 0%, 5% and 20% (all of which VFs amount to less
than 1% by mass of the multiphase flow). In other words, this
realization allows one to use the two-phase data to determine
three-phase behaviour. By measuring the differential pressure, the
liquid mass flow rate of the multiphase flow may therefore readily
be determined. Knowing this value, together with the actual bulk
density (from the Coriolis meter, corrected using the bulk density
error curve) and the pipe diameter, the actual bulk mass flow rate
of the multiphase flow at the prevailing temperature and pressure
conditions may be calculated.
[0110] Finally, the actual mass flow rate of oil is calculated.
This is done using the phase volume fractions and the actual bulk
mass flow rate. For completeness, the density of each of the
individual phases at the given temperature and pressure must also
be known, but this is information that the skilled person readily
has available.
* * * * *